MIC205A – Microbiology – Chapter 5 Questions and Answers
cost and availability of germicides some are less expensive and readily available
(hypochlorite in the form of household bleach) vs. ethylene oxide gas which is expensive and
requires a specific chamber
storage and stability of germicides some are sold as concentrated stock solutions,
decreasing the required storage space. some have a limited shelf life once prepared
environmental risk of germicides germicides that retain their antimicrobial activity after use
can interfere with wastewater treatment systems. the activity of those germicides must be
neutralized before disposal.
categories of germicidal potency sterilants, high level disinfectants, intermediate level
disinfectants, low level disinfectants
sterilants destroy all microbes including endospores and viruses (also called sporocides).
destruction of endospores requires 6-10 hour treatment. used to treat heat-sensitive critical
instruments (come into contact with body tissue)
high-level disinfectants destroy all viruses and vegetative microorganisms, but do not
reliably kill endospores. used to treat semicritical instruments (i.e. GI endoscopes)
intermediate-level disinfectants destroy all vegetative bacteria (including mycobacteria),
fungi, and most viruses. they do not kill endospores. used to disinfect non-critical instruments
(stethoscopes)
low-level disinfectants destroy fungi, vegetative bacteria except mycobacteria, and
enveloped viruses. they do not kill endospores and do not always destroy non-enveloped
viruses.
, intermediate-level and low-level disinfectants are also called... general-purpose
disinfectants; used to disinfect furniture, floors, and walls
classes of germicidal chemicals alcohols, aldehydes, biguanides, ethylene oxide gas,
halogens, metals, ozone, peroxygens, phenolic compounds, and quaternary ammonium
compounds
alcohols (ethanol and isopropanol) readily available and inexpensive, limited in contact time
due to rapid evaporation; aqueous solutions of alcohol are used as antiseptics to clean skin in
preparation for procedures that break intact skin, and as disinfectants for treating instruments
aldehydes (glutaraldehyde, ortho-phthaladehyde, and formaldehyde) capable of destroying
all microbes, but irritating to the respiratory tract, skin, and eyes. glutaraldehyde and ortho-
phthalaldehyde are used to sterilize medical instruments. formalin is used in vaccine production
and to preserve biological specimens
biguanides (chlorhexidine) relatively safe due to low toxicity. capable of destroying a wide
range of microbes. able to adhere to and persist on skin and mucous membranes.
Chlorhexidine used in products including disinfectant cleaning solutions. antiseptics used by
healthcare professionals, and prescription mouthwashes. it is also incorporated into catheters
and surgical mesh.
ethylene oxide gas capable of easily penetrating hard to reach places and fabrics. can be
used on moisture-sensitive material. toxic, explosive, and possibly carcinogenic. ethylene oxide
is commonly used to sterilize medical devices.
halogens (chlorine and iodine) chlorine is inexpensive and readily available, but organic
compounds and other impurities neutralize the activity; it may react with organic compounds,
forming toxic chlorinated products. chlorine solutions are used to disinfect inanimate objects,
cost and availability of germicides some are less expensive and readily available
(hypochlorite in the form of household bleach) vs. ethylene oxide gas which is expensive and
requires a specific chamber
storage and stability of germicides some are sold as concentrated stock solutions,
decreasing the required storage space. some have a limited shelf life once prepared
environmental risk of germicides germicides that retain their antimicrobial activity after use
can interfere with wastewater treatment systems. the activity of those germicides must be
neutralized before disposal.
categories of germicidal potency sterilants, high level disinfectants, intermediate level
disinfectants, low level disinfectants
sterilants destroy all microbes including endospores and viruses (also called sporocides).
destruction of endospores requires 6-10 hour treatment. used to treat heat-sensitive critical
instruments (come into contact with body tissue)
high-level disinfectants destroy all viruses and vegetative microorganisms, but do not
reliably kill endospores. used to treat semicritical instruments (i.e. GI endoscopes)
intermediate-level disinfectants destroy all vegetative bacteria (including mycobacteria),
fungi, and most viruses. they do not kill endospores. used to disinfect non-critical instruments
(stethoscopes)
low-level disinfectants destroy fungi, vegetative bacteria except mycobacteria, and
enveloped viruses. they do not kill endospores and do not always destroy non-enveloped
viruses.
, intermediate-level and low-level disinfectants are also called... general-purpose
disinfectants; used to disinfect furniture, floors, and walls
classes of germicidal chemicals alcohols, aldehydes, biguanides, ethylene oxide gas,
halogens, metals, ozone, peroxygens, phenolic compounds, and quaternary ammonium
compounds
alcohols (ethanol and isopropanol) readily available and inexpensive, limited in contact time
due to rapid evaporation; aqueous solutions of alcohol are used as antiseptics to clean skin in
preparation for procedures that break intact skin, and as disinfectants for treating instruments
aldehydes (glutaraldehyde, ortho-phthaladehyde, and formaldehyde) capable of destroying
all microbes, but irritating to the respiratory tract, skin, and eyes. glutaraldehyde and ortho-
phthalaldehyde are used to sterilize medical instruments. formalin is used in vaccine production
and to preserve biological specimens
biguanides (chlorhexidine) relatively safe due to low toxicity. capable of destroying a wide
range of microbes. able to adhere to and persist on skin and mucous membranes.
Chlorhexidine used in products including disinfectant cleaning solutions. antiseptics used by
healthcare professionals, and prescription mouthwashes. it is also incorporated into catheters
and surgical mesh.
ethylene oxide gas capable of easily penetrating hard to reach places and fabrics. can be
used on moisture-sensitive material. toxic, explosive, and possibly carcinogenic. ethylene oxide
is commonly used to sterilize medical devices.
halogens (chlorine and iodine) chlorine is inexpensive and readily available, but organic
compounds and other impurities neutralize the activity; it may react with organic compounds,
forming toxic chlorinated products. chlorine solutions are used to disinfect inanimate objects,
